pakfire.cgi: Add upgrade confirmation page.

pakfire.cgi: Add upgrade confirmation page.

- Add upgrade confirmation page.  Clicking on the 'Upgrade' button on the main page displays the confirmation page.

 - The upgrade confirmation page runs 'pakfire update' then displays all available core and add-on upgrades for confirmation.  If there are any 'ERROR' messages from the 'pakfire update', they are displayed on the confirmation page.

 - Changed translations for consistency:
    - 'pakfire updates' -> 'pakfire upgrades'
    - 'pakfire confirm updates' -> 'pakfire confirm upgrades'

Signed-off-by: Stephen Cuka <stephen@firemypi.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>